Crystal mounting



1950 D. w. KELLER 2,518,793

CRYSTAL MOUNTING Filed April 10, 1944 Jama Patented Aug. 15, 1950 UNITED CRYSTAL MOUNTING Dan W. Keller, Chicago, 111., assignor of one-half to Helen Keller Application April 10, 1944, Serial No. 530,278

Claims. 1

This invention relates to crystal mountings and more particularly to an electrode construction for mounting and supporting a crystal.

Heretofore crystals have been mounted between stainless steel plates cut to substantially the same size and shape as crystal with its corner portions raised and ground or lapped to fit evenly against the crystal surface. The electrical activity of crystals mounted in this manner changes materially in accordance with temperature changes and according to quite erratic curves. It is believed that this change in activity is due to the changing points of engagement between the electrode and crystal resulting from different temperature coefficients of expansion of the crystal and of the electrode material.

It is one of the objects of the present invention to provide a crystal mounting in which the crystal maintains a substantially uniform activity over a wide range of temperatures.

Another object of the invention is to provide an electrode for use in crystal mountings which has substantially the same coefiicient of expansion as the crystal to be mounted.

Still another object of the invention is to provide an electrode formed of a non-metallic body having a conductive covering to engage the crystal. In a preferred construction, the electrode itself is formed of a crystal covered by a thin sheet of metal,

The above and other objects and advantages of the invention will be more readily apparent from the following description when read in connection with the accompanying drawings, in which Figure 1 is a side elevation of an electrode constructed according to the invention;

Figure 2 is a section through a crystal mount- 7 Figure 3 is a plan View of an electrode; and

Figure 4 is a section on the line 4-4 of Figure 3, showing an alternative construction.

According to the invention a standard crystal as indicated generally at I!) in Figure 2, which may be of rectangular shape, is supported between a pair of electrodes I l which may be pressed against the crystal by springs or the like. The electrodes preferably have raised portions adjacent their corners to engage the opposite faces of the crystal.

According to the present invention the electrodes H are formed by non-metallic bodies 12 of substantially the same size and shape as the crystal to be mounted and which are made of material whose temperature coefficient of expansion is substantially the same as that of the crystal l0. Various types of materials are suitable for this purpose including certain ceramics and plastics which may be selected to have the desired coefficient of expansion. Preferably, however, the body I2 is of the same material as the crystal [0 and may be for example, a cut crystal which has been rejected for some flaw. The nonmetallic body I2 is covered by a thin conductive covering [3 extending over its entire surface. Various types of coverings may be employed but I prefer to use a thin sheet of metal either sprayed or plated directly on to the body or in the form of a metal foil covering the body and engaging it uniformly over its surface. At the corners on at least one side of the body, a double thickness of covering is provided as indicated at I4 forming raised portions to engage the opposite faces of the crystal l0. Preferably the portions I 4 are ground or lapped to engage the crystal evenly.

With electrodes of this type mounting the crystal as shown in Figure 2, the points of contact between the electrodes and the crystal will be the same under all temperature conditions since expansion of the active crystal It will be identical with the expansion of the crystal bodies l2. Therefore, the activity of the crystal [0 will be uniform throughout a wide temperature range.

Since the electrodes can be formed largely of scrap material they can be made inexpensively and will provide uniform mountings for the active crystals,

In the alternative construction shown in Figure 4, the raised corner portions indicated at I l are formed by grinding or cutting the body IE to the desired shape with its corner portions raised and uniformly plating or coating its entire surface. The final shape is the same in this construction as in Figure 1 but the covering operation is somewhat simplified. In operation the electrode of Figure 4 functions in the same manner as described above.

While one embodiment of the invention has been shown and described herein in detail it will be understood that this is illustrative only and is not intended as a definition of the scope of the invention, reference for thus purpose being had to the appended claims.

What is claimed is:

1. In a crystal mounting in combination a crystal, an electrode comprising a flat body of non-metallic material having a temperature coefficient of expansion substantially the same as that of the crystal to be mounted, and a conducting covering over the body engaging the crystal.

2. In a crystal mounting in combination a crystal, an electrode comprising a flat body of non-metallic material having a temperature coefficient of expansion substantially the same as that of the crystal to be mounted, and a thin metal covering over the body engaging the crystal.

3. In a crystal mounting in combination a crystal to 'bemounted, an electrode comprising a fiat crystalof substantially the "same size and shape and material as the crystal to be mounted and a conductive covering over said flat crystal engaging the crystal to be mounted.

4. In a crystal mounting in combination a crystal to be mounted, an elctrod'e comprising a flat crystal of substantially the same size and shape and material as the crystal .to be mounted.

and a thin metal covering over said fiat crystal engaging the crystal to be mounted.

5. In a crystal mounting in combination, a crystal to be mounted, an electrode'comprising :a flat crystal of substantially thesame size and shape and material asthe crystal to be-mounted and a conductive covering over said flat'crystal to engage the crystal to be mounted, said covering being thicker at 'spaced'points-adjacent its periphery than-over the remainder of its surface to provide raised portionsto engage the crystal to be mounted.

6. In a crystal mounting in combination, a crystalto be mounted, an electrode comprising a flat non-metallic body of substantially the same size and shape as the crystal to be mounted, said .body-beingthicker at spaced points adjacent its periphery than over the remainder of its area, and a conductive covering of substantially uniform-thickness over the body.

' '7. In a crystal mounting in combination, a crystal tobe mounted,.an electrode comprising a fiat crystal of substantially the same. size and shape. and material .as the crystal to-be mounted,

4 said flat crystal being thicker at spaced points adjacent its periphery than over the remainder of its area, and a conductive covering of substantially uniform thickness over the fiat crystal.

8. An electrode for piezoelectric crystals, said electrode comprising a crystal substantially matching in size and cut the piezoelectric crystal to which it is to be applied and having at least one face thereof covered with electrically conductive material. 1

9. An electrode for piezoelectric crystals, said electrode comprising a platelike core of nonconductive material having a coefficient of thermal expansion substantially matching that of the piezoelectric crystalwith which it is to be used and having at least one face thereof covered with electrically conductive material.

10. An electrode for piezoelectric crystals, said electrode comprising a generally rectangular plate-like core of crystalline quartz wrapped in a thin metal foil which is electrically conductive, and additional layers of material fixed to the corner portions of one face of the wrapped core totconstitute feet for the same.

DAN W. KELLER.

REFERENCES CITED The following referencesare ofirecord in'the file of this patent:

UNITED STATES PATENTS Number Name Date 1,692,074 Burtis Nov. 20, 1928 1,908,320 Conklin May 9, 1933 2,978,229 Bokovyet a1 Apr. 27, 1937 FOREIGN PATENTS Number Country Date 490,085 Germany Jan. 23, 1930 490,579 Germany Jan. 30, 1930 

